Commit 763e4cdc authored by Brian Foster's avatar Brian Foster Committed by Darrick J. Wong
Browse files

iomap: support partial page discard on writeback block mapping failure 



iomap writeback mapping failure only calls into ->discard_page() if
the current page has not been added to the ioend. Accordingly, the
XFS callback assumes a full page discard and invalidation. This is
problematic for sub-page block size filesystems where some portion
of a page might have been mapped successfully before a failure to
map a delalloc block occurs. ->discard_page() is not called in that
error scenario and the bio is explicitly failed by iomap via the
error return from ->prepare_ioend(). As a result, the filesystem
leaks delalloc blocks and corrupts the filesystem block counters.

Since XFS is the only user of ->discard_page(), tweak the semantics
to invoke the callback unconditionally on mapping errors and provide
the file offset that failed to map. Update xfs_discard_page() to
discard the corresponding portion of the file and pass the range
along to iomap_invalidatepage(). The latter already properly handles
both full and sub-page scenarios by not changing any iomap or page
state on sub-page invalidations.

Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 869ae85d

fs/iomap/buffered-io.c

+8 −7
Original line number Diff line number Diff line
@@ -1382,14 +1382,15 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc, 
	 * appropriately.

	 */

	if (unlikely(error)) {

		if (!count) {

		/*

			 * If the current page hasn't been added to ioend, it

			 * won't be affected by I/O completions and we must

			 * discard and unlock it right here.

		 * Let the filesystem know what portion of the current page

		 * failed to map. If the page wasn't been added to ioend, it

		 * won't be affected by I/O completion and we must unlock it

		 * now.

		 */

		if (wpc->ops->discard_page)

				wpc->ops->discard_page(page);

			wpc->ops->discard_page(page, file_offset);

		if (!count) {

			ClearPageUptodate(page);

			unlock_page(page);

			goto done;

fs/xfs/xfs_aops.c

+8 −6
Original line number Diff line number Diff line
@@ -527,13 +527,15 @@ xfs_prepare_ioend( 
 */

static void

xfs_discard_page(

	struct page		*page)

	struct page		*page,

	loff_t			fileoff)

{

	struct inode		*inode = page->mapping->host;

	struct xfs_inode	*ip = XFS_I(inode);

	struct xfs_mount	*mp = ip->i_mount;

	loff_t			offset = page_offset(page);

	xfs_fileoff_t		start_fsb = XFS_B_TO_FSBT(mp, offset);

	unsigned int		pageoff = offset_in_page(fileoff);

	xfs_fileoff_t		start_fsb = XFS_B_TO_FSBT(mp, fileoff);

	xfs_fileoff_t		pageoff_fsb = XFS_B_TO_FSBT(mp, pageoff);

	int			error;



	if (XFS_FORCED_SHUTDOWN(mp))
@@ -541,14 +543,14 @@ xfs_discard_page( 


	xfs_alert_ratelimited(mp,

		"page discard on page "PTR_FMT", inode 0x%llx, offset %llu.",

			page, ip->i_ino, offset);

			page, ip->i_ino, fileoff);



	error = xfs_bmap_punch_delalloc_range(ip, start_fsb,

			i_blocks_per_page(inode, page));

			i_blocks_per_page(inode, page) - pageoff_fsb);

	if (error && !XFS_FORCED_SHUTDOWN(mp))

		xfs_alert(mp, "page discard unable to remove delalloc mapping.");

out_invalidate:

	iomap_invalidatepage(page, 0, PAGE_SIZE);

	iomap_invalidatepage(page, pageoff, PAGE_SIZE - pageoff);

}



static const struct iomap_writeback_ops xfs_writeback_ops = {

include/linux/iomap.h

+1 −1
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ struct iomap_writeback_ops { 
	 * Optional, allows the file system to discard state on a page where

	 * we failed to submit any I/O.

	 */

	void (*discard_page)(struct page *page);

	void (*discard_page)(struct page *page, loff_t fileoff);

};



struct iomap_writepage_ctx {

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